Color reproduction processes typically involve using color imaging systems to produce colors on various media. These color imaging systems may be used to duplicate a color image from one medium to another medium, e.g., from one printed copy to another or from a display screen to a printed copy. Color reproduction processes are used in various application environments, for example, color proofing applications.
Some color reproduction processes use approaches known as color management systems (CMSs) to characterize various color imaging systems and to transform color data between the color imaging systems. Characterizing color imaging systems typically involves calculating color response functions using color coordinate systems known as color spaces. One commonly-used color space is Commission Internationale de l'Éclairage L*a*b* (CIELAB) space. CMSs attempt to reproduce an original color image on a color imaging system so as to preserve the appearance of colors between the original and the reproduction within the limitations of the color imaging system of the reproduction process.
Various CMS approaches have been proposed to achieve accurate color reproduction. Many of these approaches involve producing color samples using an output or display device and measuring the color values of the samples using an input device. Such approaches correlate the output colors with the measured color values. This correlation is performed using, for example, forward and reverse transforms between device-specific color spaces and a device-independent color space. These transformation techniques are often supplemented by interpolation between entries in a multidimensional lookup table. These techniques exhibit inaccurate color conversion between similar devices, potentially resulting in undesirable contamination of colors. Furthermore, accurate color conversion of dark colors has often been particularly difficult because of inadequate processing of black channel data in many applications.
CMSs often perform gamut mapping to correlate the range or gamut of colors that can be realized by a device with regions of a color space. Because many devices are incapable of realizing the complete range of colors in a color space, gamut mapping typically involves compressing or scaling regions of the color space. The device can then approximate colors outside its gamut using the compressed regions of the color space. For many CMSs, gamut mapping is potentially inconsistent under certain circumstances, such as when using profiles generated by software from different vendors. In addition, many CMSs exhibit inconsistencies when performing forward and reverse transformations between imaging systems. For example, color shifting often occurs with repeated forward and reverse transformations.
Many CMS techniques exhibit other limitations in addition to the lack of accuracy in converting colors. For example, many CMS techniques are relatively inflexible with respect to changes in illumination and observer conditions, gamut mapping, and choice of color space. Certain techniques lack forward compatibility with future color standards.